The present invention relates to a method and apparatus for attaching filter plugs (e.g., filter plugs of double unit length) to rod-shaped tobacco-containing articles such as plain cigarettes, cigars or cigarillos. More particularly, the invention relates to improvements in treatment or processing of the filter plugs, especially of so-called NWA filters, prior to their attachment to plain cigarettes or the like.
It is well known to produce filter cigarettes in a so-called filter tipping machine (e.g., a machine known as MAX S, produced by the assignee of the present application) wherein pairs of plain cigarettes are connected to filter plugs of double unit length by adhesive-coated uniting bands which are convoluted about filter plugs and about the adjacent inner end portions of plain cigarettes. During convoluting, groups of three coaxial rod-shaped articles (including two spaced-apart plain cigarettes of unit length and a filter plug of double unit length therebetween) are caused to advance through a gap which is defined by two surfaces moving relative to each other and whose width is less than the diameters of articles in a group so that the groups are caused to roll about their respective axes and convert originally flat sheet-like uniting bands into tubes which sealingly connect the filter plugs to the respective pairs of plain cigarettes. The resulting filter cigarettes of double unit length are thereupon severed to yield pairs of filter cigarettes of unit length. Uniting bands are attached to successive groups during travel of such groups in the flutes of a transfer conveyor which delivers the groups (each of which carries a non-convoluted uniting band) to the components serving to roll the groups about their respective axes.
The uniting bands are obtained by severing the leader of a web of cigarette paper, artificial cork or like wrapping material at regular intervals subsequent to coating of one side of the web with a suitable adhesive. Such uniting bands normally establish fluidtight seals between the filter plugs and the adjacent plain cigarettes, especially if the filter plugs are of the type wherein a cylindrical section consisting of filter material (such as filamentary filter material and/or granular filter material) is surrounded by a tubular wrapper of cigarette paper or the like. The adhesive-coated sides of uniting bands readily adhere to the wrappers of filter plugs as well as to the wrappers (tubes consisting of cigarette paper) of plain cigarettes.
Problems arise when the filter plugs which are used in the manufacture of filter cigarettes, cigars or cigarillos do not have distinct wrappers, i.e., when the tobacco-containing rod-shaped articles are attached to so-called NWA filters. The unrwapped peripheral surfaces of NWA filters (hereinafter called unwrapped filters) are not smooth because such surfaces are formed by the rather coarse filamentary filter material, normally fibers consisting of synthetic thermoplastic material. Moreover, the peripheral surfaces of unwrapped filters are not as uniformly convex or round as the peripheral surfaces of wrappers on conventional filter plugs.
On the other hand, unwrapped filters or filter plugs are preferred in many presently popular brands of filter cigarettes or the like because they facilitate the manufacture of rod-shaped smokers' products with so-called ventilation or climatic zones, namely, filter cigarettes, cigars or cigarillos (hereinafter referred to as filter cigarettes) wherein the wrappers exhibit a certain degree of permeability to allow predetermined quantities of cool atmospheric air to penetrate through the wrappers and to mix with the columns of tobacco smoke. The permeability of unwrapped filter plugs (as considered in the radial direction thereof) is much more pronounced and more uniform than the permeability of wrappers of conventional filter plugs. Furthermore, ventilation or climatic zones can be estalished by the simple expedient of utilizing uniting bands whose material exhibits a predetermined porosity. Such porosity determines the so-called degree of ventilation of finished filter cigarettes.
Since the peripheral surfaces of unwrapped filter plugs are rough (i.e., rougher than the peripheral surfaces of wrappers forming part of conventional filter plugs), the adhesive-coated uniting bands are much less likely to adhere to the peripheral surfaces of unwrapped filter plugs. It has been found that uniting bands are likely to be shifted relative to and/or to become fully separated from the respective groups of rod-shaped articles during introduction into and/or during travel through the aforediscussed gap wherein the uniting bands are supposed to be converted into tubes which connect filter plugs to the respective plain cigarettes. This results in the production of substantial numbers of rejects which is especially undesirable in modern high-speed filter tipping machines.